To achieve so-called interworking, i.e. a transfer of data between networks with differing protocol structures, particularly between ATM networks and Ethernet networks, it is necessary to adapt the data flow and/or the data structure of transmission units between the network protocols concerned.
ATM network protocols provide for data to be transmitted in transmission units in the form of ATM cells with a fixed length. An ATM cell comprises a header section and a payload section, in which the header section contains administrative information. The data charge itself is contained in the payload section. ATM networks usually use payload sections of 48 bytes. Adaptation protocol layers which provide the transition to higher level protocols, e.g. AAL5 (ATM Adaptation Layer 5), provide for several ATM cells to be joined together into higher level transmission units. The higher level transmission units have no fixed length. The higher level transmission units are broken down into ATM cells for transmission and reassembled after transmission, i.e. brought back together.
In Ethernet networks, e.g. fast Ethernet networks or gigabit Ethernet networks the data is transmitted in transmission units in the form of Ethernet frames. The Ethernet frames may have variable length, typically greater than the length of the ATM cells described above.
For interworking, for example between an ATM network and an Ethernet network it is therefore necessary to adapt the data structures of the transmission units between the network protocols involved. This means that transmission units of one network protocol with a specific characteristic length have to be converted into transmission units of the other network protocol, whereby the transmission units of the other network may have a different length, which may vary from transmission unit to transmission unit. In the opposite direction, transmission units of the other network protocol have to be converted into transmission units of the first network protocol. In addition, the concatenation of transmission units into higher level transmission units has also to be taken into account in the conversion process. This conversion is generally carried out by a corresponding electronic storage and processing of the transmission units, which is associated with considerable effort. This is also associated with a correspondingly complex structure of an interworking device used for this purpose, e.g. in the form of a semiconductor network communications component.
It is an object of the present invention therefore to provide a process for the storage of transmission units and a corresponding network communications device which will solve the problem described above and particularly enable efficient storage and processing of the transmission units of various network protocols.
This object is achieved by a process according to embodiments of the present invention and by a network communications device according to embodiments of the invention.